1. Field of the Invention
The present invention relates generally to a fluid flow control system, and is directed more particularly to a novel speaker system which is driven by a pluse code modulation signal to produce an acoustic output directly.
2. Description of the Prior Art
In general, prior art speakers have a very small acoustic radiation resistance. For example, the winding resistance of the voice coil of an electro-motive type of speaker is several thousand times as great as the acoustic radiation resistance of that speaker. Thus, the acoustic-conversion efficiency of such a speaker is reduced by thermal loss. The acoustic radiation resistance of an electro-static type of speaker that uses a vibrating plate as the electro-acoustical transducer element is very small as compared with the reactance component of the vibrating plate, which also results in mis-matching, and hence, in reduced efficiency.
In prior art speakers utilizing a vibrating plate, it is well-known that the vibrating plate is subjected to divided vibrations in various and complicated modes, so that the sound is distorted. In electro-motive speakers, a further distortion is produced by the non-linearity of the magnetic circuit of the speaker. In general, even if the vibrating plate of a speaker is designed to have as large a damping factor as possible, the vibrating plate has inerita. Therefore, when a pulse signal, for example, is fed to such a speaker, the acoustic output therefrom has a damped oscillation waveform.
As described above, prior art speakers have low efficiency and high distortion characteristics as compared with those of other acoustic components, and hence limit the possibility of improving the fidelity of the whole acoustic reproduction system.
Further, a reverse sound pressure is produced behind the vibrating diaphram of prior speakers, so that a large baffle plate is necessary to prevent the reverse phase sound pressure from being transmitted to the front side of the speaker. As a result, it is difficult to generate low frequency sounds by means of a small size speaker.
At present, a PCM technique is employed in the audio field. That is, an audio signal, such as a voice signal, a musical signal, or the like, is converted into a PCM pulse signal and then recorded and reproduced. According to this PCM technique, an audio signal can be reproduced with higher difelity than can the same signal recorded and reproduced by prior art analog treatment. However, even if the PCM technique is employed in recording and transmission systems, the reproduction system (speaker and so on) at the terminal end of the prior art reproduction system must be only by analog signal. Thus, it is still necessary to convert the PCM signal into an analog signal in the prior art.
Devices that utilize fluid flow in digital systems are known as fluidic devices. Certain basic fluidic devices are described in an article entitled "Fluid Amplifiers - New Dimension for Fluid Power," Henry Lefer, Hydraulics & Pneumatics, February, 1965, pp. 61-64.